A handheld power tool such as a hammer drill, a chisel hammer or a rotary hammer drill or combination hammer, has a striking mechanism that is capable of transmitting a pulse impact at a suitable repeat rate to a tool that is secured in the handheld power tool. For this purpose, the above-mentioned striking mechanism has a drive that acts directly or indirectly so as to accelerate a movable striking-mechanism body such as, for instance, a striker or a striking pin. The drive of the striking mechanism can be configured, for example, with an eccentric wheel mounted on a drive bearing, said wheel causing a piston to execute a stroke motion that then drives the striker, for instance, pneumatically, so that it executes a back-and-forth motion and this, in turn, acts on the striking pin. Therefore, the directly driven striker of the striking mechanism first transmits a pulse impact to the striking pin and then from the striking pin to the shank of the tool.
The striking-mechanism body has a lateral surface and an impact surface. The pulse impact of the striking-mechanism body against the impact surface is regularly transmitted to a pulse-receiving part. The pulse-receiving part can be a tool of the handheld power tool, for instance, a drill bit or a chisel, that receives the pulse impact against the head surface of a tool. Pulse-transmitting impact surfaces serve primarily to transmit pulses between striking-mechanism bodies inside the striking mechanism, in other words, for example, between a striker and a striking pin. Parts of the striking mechanism have to be able to withstand relatively high stresses, especially on an impact surface and/or on a lateral surface.
A striking-mechanism body is known which is made of a case-hardened steel or tempered steel that has been treated, for example, in its entirety by means of case-hardening or tempering or by means of some other heat treatment and that, as such, has identical properties in a single piece along the entire striking-mechanism body, especially also identical properties on the impact surface and on the lateral surface. It has been shown, however, that a striking-mechanism body is exposed in different areas to different stresses, thus making different requirements of the material of the striking-mechanism body. As the energy density in a striking mechanism increases, that is to say, as the ratio of the energy input to the dimensions of a striking-mechanism body increases, the more stringent the requirements become. Thus, for instance, in Japanese laid-open document JP 101 69 358 A, an attempt is made to increase the energy density in a striking mechanism by increasing the specific density of the striking-mechanism body. Even when very high-grade materials and conventional heat-treatment methods are employed for the striking-mechanism body, excessive stresses and premature material fatigue ultimately cannot be avoided at the highest energy densities. The decisive factor is the pulse of a striking-mechanism body—resulting from the velocity and the moved mass—in relation to the resistance of the material of the striking-mechanism body, especially its impact surface and/or lateral surface. Moreover, large striking masses of a striking-mechanism body always translate into a larger installation space for the striking mechanism in terms of its diameter and length, thus leading to larger and possibly disproportionally heavy machines.
For instance, international document WO 99/67063 discloses measures that attempt to reduce the weight of a drive piston for an air-spring striking mechanism in that the piston suspension is made of a plastic material. Moreover, U.S. Pat. No. 3,114,421 or Japanese laid-open document JP 2006 123025 A disclose other measures for adjusting the mass of the striking-mechanism body by selecting different material densities. These measures, however, are inadequate since, on the one hand, only an insufficient bond can be achieved among different masses of parts of the striking mechanism. In any case, on the other hand, the most heavily stressed areas of a striking-mechanism body, namely the impact surfaces and the lateral surfaces, turn out to be insufficiently resistant. Alternatively, Japanese laid-open document JP 8197458 A or German patent application DE 103 044 07 A1 or German document DE 922 038, for example, disclose striking-mechanism bodies having cavities which, when filled with plastic particles or individual particles, have a damping effect on the motion of the striking-mechanism body.
Such measures cannot offset negative effects such as so-called reverberation or the generation of excessive tensile stresses in the tool being used. Negative effects such as, for example, spark discharge as described in Japanese laid-open document JP 10156757 A, can only be prevented to a limited extent in that parts made of a beryllium-copper compound or reinforced plastic are glued or welded onto the colliding parts of a striker and of a striking pin. Such parts cited in JP 10156757 A, however, regularly prove to be insufficiently resistant.